The present invention relates to a surface mountable laminated thermistor device, specifically to a surface mountable laminated thermistor device having a Positive Temperature Coefficient (hereafter referred as PTC) characteristic.
PTC device has been widely applied in the fields of temperature detection, safety control, temperature compensation, etc. In the past, thermistor device was primarily made from ceramics. High temperature is needed in fabricating ceramics and the temperature used in the fabrication process is usually higher than 900 degrees Celsius, which complicates the process and consumes large amount of energy. Polymeric thermistor device was then developed. Since the fabrication temperature for a surface mountable laminated thermistor device with polymer-based material is lower than 300 degree Celsius, it can be understood that the process and formation becomes easier because energy consumption is lesser, fabrication process is simpler and the cost is lowered compared to the fabrication process described previously. Therefore, the application fields are gradually broadened.
The conventional PTC circuit protection device can be made by using polymeric composite materials filled by conductive fillers. It can be applied in the current overloading protection device and the design of the temperature-switching device. This is due to the fact that the conductive filling particles in the polymeric composite material filled by the conductive filler are at the conducting state of connecting to each other at room temperature. When the temperature rises above the switching temperature, the volume of the resin material in the polymeric composite material expands, causing conductive filling particles in the polymeric composite material to transform from the state of connecting to each other to expand to break to become an discontinuous state so as to cause the resistance of the PTC circuit protection device to rise rapidly to cut off the current, thereby achieving the objectives of current overloading protection and temperature-controlled switch. Carbon Black is often used as conductive fillers.
The conventional PTC laminated structure uses the conductive composite material component with a top layer and a bottom layer metal foils and an intermediate layer with the PTC characteristics. It arranges with a lateral conductive mechanism and an insulating material to electrically conduct the top layer and bottom layer metal electrodes of the conductive composite material component with the PTC characteristics to another plane to make the surface mountable circuit protection device.
These techniques mainly adopt the metal foils and the conductive composite material components with the PTC characteristics. The PTC laminated structure is formed after the thermal laminating, then electroplating, etching, plated through hole, and dipping electroplating processes are conducted. First of all, the metal foils, the conductive composite material component with PTC characteristics, and the PTC laminated structure formed by thermal laminating metal foils have insufficient mechanical strength, and are prone to wrapping to deform during the above processes. After circuits are made, thermal laminating of other PTC laminated structures, the insulation reinforcement material or the metal electrode to form multiple-layer PTC laminated structure will cause the problem of how to align top and bottom layers accurately. On the other hand, the technologies described above when use the metal foil and conductive composite material with the PTC characteristics are processed, because of the material is flexible so the shortcomings of possible wrapping during the processing, deformation, poor dimension stability, and uneasy processing are more likely to occur.
In addition, designing a surface mountable laminated thermistor device in a way such that the device having conductive polymeric composite material with PTC characteristics may achieve parallel effect because of circuit connection design combinations when resolving this fabrication and processing problems is also one of the industrial needs. Thus, the application field of surface mountable laminated thermistor device can be broadened.